Just to confirm that I have the understanding of the issue; The desired behaviour would be to enter prices in the back-end exclusive of tax, and then they would display with tax added on the shopfront (before the checkout is reached)?

EU laws require us to always show prices including VAT.
It would be easy to add this functionality in the admin, please consider it for the next release. I think that all EU shop owners would be happy if OC comes with this functionality.

OSWorX: You really dont want to understand this do you?
You keep talking about companies only have to use net prices and that VAT is some extra amount you just pay to the tax office.
Opencart are not an accounting software, its mostly used to sell stuff, and often to consumers and therefore you adjust your prices accordingly so the price is nicely rounded to appeal to consumers. You know, 99 is better than 100 and so forth. Take 99 for instance, without (25% swedish) VAT the price is 79,20, not very easy to know without calculating first.
You dont want to use a calculator each time you update a price or make a new product, its much easier to use the price including VAT.
Often as a reseller you get a recomended retail price from your distributor that you may want to use, you then now exactly what the price with VAT should be and it would be so much easier to just write it including VAT directly.
This has nothing to do with calculating your margins and so on, that of course you have to do regardless, its just that its so much easier to use the rounded retail price including VAT when you sell to consumers.

Why shouldnt this be an option in the core, its superstrange to me.
I know i can get extensions that do this, i have it in my shop and it is really helpful. But i really think this is such a elementary function that should be in the core.

If I change all my prices to include VAT then business customers will be put off my the higher costs, they most likely not realise that they can knock 20% off the costs. My competitors have cart systems that show both.